The invention is drawn to the genetic manipulation of plants, particularly to enhancing pathogen resistance in plants.
Plant pests result in losses to farmers which run into millions of dollars per year. The rising costs of pesticides, the increasing resistance of insects to pesticides, and their undesirable effects on the environment, stresses the need to exploit host plant resistance to pests and diseases. In the past, pathogen disease resistance was handled by conventional crop breeding, which while sophisticated is time consuming and expensive. While various xe2x80x9cgenetic engineeringxe2x80x9d strategies for enhancing pathogen resistance have been proposed, and some are showing success, the record has been spotty and no single general strategy has emerged that bears consistent success. In fact, there may not be a single strategy that will work against all pathogens, or that will work in all plants given the evolutionary dynamics of plants and pathogens. Providing seed producers and growers with a variety of weapons to choose from is to their advantage. Thus, additional mechanisms are needed to protect plants against plant pests.
xcex2-glucosidases catalyze the hydrolysis of glycosidic linkages in aryl and alkyl xcex2-glucosides and cellobiose and occur ubiquitously in plants, fungi, animals and bacteria. Maize xcex2-glucosidase is an abundant soluble protein in young, growing plant parts. In seedlings, xcex2-glucosidase activity has been found mainly in coleoptiles and mesocotyls and, to a lesser extent, in roots. One physiological function for maize xcex2-glucosidase is the hydrolysis of the hydroxamic acid glucoside (for example 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3-one glucoside DIMBOA-glc=DIMBOA glucoside). The hydrolysis reaction releases a biologically active free form of the compound from its conjugated form.
Hydroxamic acids derived from 4-hydroxy-1,4-benzoxazin-3-one are secondary compounds produced in cereals such as maize, wheat and rye, and in other Gramineae. Upon disruption of the tissue, hydroxamic acids are liberated which are chemically labile and of higher toxicity than the parent glucosides. Hydroxamic acids play a major role in the defense of the plant against insects such as the European corn borer, Ostrinia nubilalis, the western corn root worm, Diabrotica virgifera, and cereal aphids and pathogens such as corn leaf blight (Helmintho sporium) and stalk rot (Diplodia magdis). The concentrations of hydroxamic acids in a given tissue of the plant and in the plant as a whole decrease as the tissue or plant age, thereby rendering the plant more susceptible to pathogen attack. xcex2-d-glucohydrolysis is catalyzed by xcex2-glucosidase, and therefore may be a decisive factor in regulating the concentration of hydroxamic acids and thereby promoting plant pathogen resistance.
Methods for enhancing disease resistance of plant cells and plants are provided. The methods comprise transforming a plant cell with a DNA construct comprising a promoter operably linked to a nucleotide sequence encoding a xcex2-glucosidase. Methods provide for increased expression of the xcex2-glucosidase sequence in the plant, thereby providing enhanced disease resistance. The xcex2-glucosidase coding sequence may be expressed utilizing various promoters to control the tissue or temporal specificity of the protein in the transformed plant.
Transformed plants, plant cells, and tissues, having altered xcex2-glucosidase levels are also provided. Such plants exhibit increased pathogen and disease resistance.